The present invention relates to digital imaging and, more particularly, to a method of digitally manipulating the inking in an image in order to obtain a high quality print image with a favorable inking application, for any multicolor printing device.
Ink jet printing systems are known in which a print head defines one or more rows of orifices which receive an electrically conductive recording fluid, such as for instance a water based ink, from a pressurized fluid supply manifold and eject the fluid in rows of parallel streams. Printers using such print heads accomplish graphic reproduction by selectively charging and deflecting the drops in each of the streams and depositing at least some of the drops on a print receiving medium, while others of the drops strike a drop catcher device.
Adapting traditional black-and-white technology to a full color printing process introduces unique problems. Four-color printing (cyan, magenta, yellow and black) places much more ink on the paper than black and white printing. The high water content of continuous ink jet inks makes this a particular problem, with noticeable negative effects. For instance, excessive inking causes the substrate to wrinkle. If too much ink is put onto the page, the ink seeps through to the reverse side of the paper. If the paper cannot be dried before it reaches the take-up roller, wet ink will rub off onto subsequent sheets. Also, ink can soak into the page and cover a larger area than intended. Large amounts of water in confined areas cause some areas of the paper to stretch, which makes it difficult to properly align all four printheads. Finally, colored ink is more expensive than black ink, and therefore less desirable to waste or reprint.
It would be desirable then to be able to maintain high quality of image saturation and density while reducing the amount of ink applied to the paper.
The present invention proposes a method of digitally manipulating inking in digital images to reduce the amount of ink put on the paper. Traditional methods of ink reduction, such as under color removal and grey component replacement attempt to reduce the total amount of ink in the image by taking advantage of the fact that cyan, magenta and yellow, mixed together, form a greyish color. Grey, then, can easily be represented by a percentage of black. Unfortunately, these traditional methods can cause color shifts in areas where the colored inks are not approximately equal, and can leave some colors unmanipulated that could have been used under color removal. Additionally, the results vary depending on the device used and the substrate used. The present invention overcomes all of these problems by replacing some inkings with values determined from actual measurement, rather than with values derived from formulas.
In accordance with one aspect of the present invention, digital image data is manipulated by means of multiple transformations, maintaining printed color quality while obtaining a more favorable inking. The technique of the present invention of manipulating inking is calorimetric, in that it is based on precise color measurements. In the existing art, methods of manipulating inking are based on theoretical behavior of inks and colors, while the method of the present invention is based on hard data for the particular print system.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.